1. Field of the Invention
The invention relates to a fire blocking device as indicated in claim 1, in particular for blocking flames, which can be transferred through ventilation grates and similar apertures with air transfer. With “fireblocking device” is here ment a passive element, open for air transfer, which prevents the spreading of fire by penetration of flames, heat conduction, convection or radiation.
2. Description of Related Art
Open flame arresters are known, which function as heat sink for explosive combustion or short-lived fireballs. They are arranged open, so that air transfers, but not flames. They are often made of steel, either as perforated plates or mesh or as steel strip bodies pressed together, and similar. The function of arresting deflagration combustion first became known as Davy's net in 1815, used by Sir Humphrey Davy, and such elements have been used for different industrial purposes, such as for engine block ventilation and in gas production facilities, as explosion flame shields for personal safety offshore and similar.
Building fires are in some instances transferred by flames spreading through openings and channels containing or being adjacent to combustible elements or materials.
An example of such a risk in buildings are the inlets to ventilated, non-heated roofs (voids) or attics, where flames on the outside of a wall or from a window, can spread through ventilators in eaves and into combustible structures in attics. Such areas are not easy accessible, and fires that take hold here, often result in dramatic consequences.
Such fire spreading is hard to stop, and thus far one has not considered it possible to combine the demand for venting and fire resistance. Activateable dampers are considered to be too unsafe because flames can pass for minutes before closing, because of the weathering, because of mechanical and movable parts and because of dry materials, which can ignite before closing.
From U.S. Pat. No. 5,565,274 (Perrone et al.) it is known for instance an attic hatch, which comprises intumescent material and which is closed with a heat-triggered activator.
From U.S. Pat. No. 5,811,731 (Jacques et al.) it is known to line an intumescent material around a cable channel. There are vents for conducting excess heat from cables and a steel grille, which will be disintegrated in case of a fire.
Known patents and solutions for preventing fire spreading in openings for air passages have a weakness in that, during a period before they are activated, they allow flames to pass through and ignite combustible gas or easily ignitable solid materials on the side that shall be protected. Some of them also leave cracks, which make flame tongues and smoke spreading possible, even when they are closed.